One conventional construction for such a lamp incorporates a base with a frame mounted above the base for rotation. A motor mounted to the frame is adapted to rotate therewith, the motor shaft being connected to a reducing gearbox which typically reduces a motor speed of about 2500 rpm to an output speed of about 45 rpm. The output from the gearbox drives a pinion gear which engages a larger stationary gear concentric with the axis about which the frame rotates.
An important disadvantage in the conventional construction just described relates to the relatively complex and expensive gearbox necessary to accomplish the 50:1 reduction required. The gearbox usually contains several gears in a gear train.
Conventional constructions also incorporate sliding ring contacts for transmitting electrical power to the motor and to the lamps mounted on the frame. As is well known, sliding contacts generate radio interference, and when flashing lamps of this kind are mounted on emergency vehicles that need to be in constant and reliable radio contact with a central dispatch or office, such radio interference can be not only annoying but dangerous.